This invention relates to "thick films" as that term is used in the electronics industry to differentiate over ultra-thin films of the type that are formed by vacuum deposition and sputtering, etc. "Thick films" are those formed by such processes as spraying, silk screening, painting, etc.
Silver powders, like other conductive metallic powders, are often used in forming conductive masses, especially conductive coatings. There are numbers of silver powders (and compositions containing such silver powders in liquid vehicles) used in the prior art for formation of conductive coatings. Many of these materials are well known commercial products, e.g. of the type sold by the Photo Products Department of E. I. DuPont de Nemours & Co. These commercial materials are sintered at temperatures in the range of 480.degree. C. to 950.degree. C. in order to achieve the adhesion and conductivity characteristics required by the electronics industry. Such elevated temperatures require slower processing procedures and limit the kind of materials with which the coatings can be adequately utilized. Indeed, at these temperatures, differential thermal expansion of substrate and coating often dictate the processing time cycle.
These powders of the prior art are typically of two microns or more in nominal particle size. It is believed that this particle size contributes to the inability of points formed of such powders to be formed in thin lines, i.e. lines having a resolution of less than the range of about 0.003 inches to 0.005 inches in width.
Of course, it is known that smaller particles of metals may be produced by reduction of carboxylate salts such as oxalates, formates and the like. However, it has remained a problem to obtain and utilize such powders in a highly conductive form, especially at lower temperatures.